Zeigler Natta (“ZN”) impact copolymers (“ICPs”) have enjoyed considerable success in the marketplace in spite of structural deficiencies inherent in their design due to the complex multi-sited nature of the ZN catalysts and the multi-step process itself. Two decades of research in this area suggests that post-reactor modification is one way to significantly differentiate the ZN-ICP from other reactor blends (in-situ) or physical melt-blends (ex-situ). Even further, ex-situ blends may replace common in-situ ICP's due to the inherent ability to tailor the polymers while in the melt. It is known for example that certain peroxides, especially organic peroxides, can be used to visbreak polypropylenes, and cross-link polyethylenes. The inventors here demonstrate that post-reactor modification of the polypropylene portion of a polypropylene-based ICP through treatment with short half-life organic peroxides can offer a significant performance improvement.
Relevant publications include EP 2 679 630 A1; EP 2 000 504 A1; U.S. Pat. Nos. 5,883,151; 6,875,826; 6,573,343; US 2003/0157286; WO 1997/49759; WO 1999/27007; WO 1994/005707; and WO 2014/070386; as well as:                M. H. Wagner et al., “The strain-hardening behaviour of linear and long-chain-branched polyolefin melts in extensional flows,” in 39 RHEOL. ACTA 97-109 (2000);        N. Spisakova et al., in 15 J. MACRM. SCI. & APP. CHEM. 37 (2000);        R. P. Lagendijk et al., in “Peroxydicarbonate modification of polypropylene and extensional flow properties,” in 42 POLYMER 10035-10043 (2001);        M. Ratzsch et al., 27 PROG. POLYM. SCI. 1195 (2002);        P. Spitael et al., in “Strain hardening in polypropylenes and its role in extrusion foaming,” in 44(11) POLY. ENG. & SCI. 2090-2100 (2004);        P. Iacobucci, “High melt strength polypropylene through reactive extrusion with Perkadox 24L,” SPE POLYOLEFINS CONFERENCE, Houston, Tex. (February 2004);        K. Jayaraman et al., “Entangling additives enhance polypropylene foam quality,” in SPE PLASTICS RESEARCH ONLINE (2011); and        H. Pol et al., “Microstructure and rheology of high-melt-strength poly-(propylene) impact copolymer,” in SPE PLASTICS RESEARCH ONLINE (2014).        